Stabilized phosphoric acid



United States Patent 3,269,798 STABILIZED PHOSPHORIC ACID John MilesPreston, Box 292, Gilrnan, Ill.

No Drawing. Original application Jan. 26, 1962, Ser. No. 169,126.Divided and this application Aug. 20, 1964, Ser. No. 397,057

7 filaims. (Cl. 23-165) This is a division of application Serial No.169,126, filed January 26, 1962, and now US. Patent No. 3,183,- 073.

This invention relates to an improved liquid fertilizer composition andto a method for preparing such fertilizer compositions.

Liquid fertilizers of a concentrated nature have been producedheretofore but difficulty has been experienced in their salting outparticularly at low temperatures, say, below the freezing point ofwater. For example, a fertilizer composition having an analysis of0-26-26 (percent by weight of N, P 0 K 0), although a highlyconcentrated plant food, will salt out at room temperature. Anyprecipitation of solids in the liquid will clog the spraying nozzleswhich are used to apply the fertilizer to the land, or the drainopenings in holding tanks. If the solids are permitted to settle to thebottom so that only the supernatant liquid is used, there is no cloggingproblem but the concentration of the plant food is substantially reducedas compared with the original composition.

In accordance with the present invention, this salting out, or settlingof solid materials from the liquid, can be reduced so that thecomposition is relatively stable at temperatures even below freezing. Ifthe fertilizer is intended to be used at normal temperatures, say above50 F., the concentration can be proportionately increased as comparedwith liquid fertilizer compositions proposed heretofore. By increasingthe concentration more plant food is present in any given volume of theliquid fertilizer. Hence, in accordance with this invention liquidfertilizer solutions can be prepared in which the salts remain insuspension or solution at much higher concentrations than heretoforepOSSible without settling out. In concentrated form the fertilizeroccupies one-third the Volume of a conventional composition. The savingsin transportation and storage are at once apparent. The farmer usingsuch fertilizer makes fewer trips over the field, thus minimizing damageto plant life or the soil structure.

This improved stability may be obtained by adding to the composition asmall quantity of glucose or a sugar or other carbohydrate whichhydrolizes to form glucose. Although the ultimate composition is highlyalkaline, it has been found desirable to add the sugar orglucoseproducing material to the acid prior to admixture with thealkaline portion of the fertilizer composition. I have found thatsucrose, maltose and lactose, all disacchaiides, are suitablestabilizing additives. As indicated glucose, a monosaccharide, isoperable; but I have found that fructose, a monosaccharide, of aslightly different molecular structure, is not operable, at least incomparable concentrations. In preparing the compositions of theinvention from high grade furnace phosphoric acid and potassiumhydroxide, colloidal or microcrystalline particles may be present in theliquid but remain suspended due to the presence of the stabilizing agentso that it remains a free-flowing solution or suspension of uniformconcentration.

In the preferred process of the invention, a small quantity of a sugar,from 0.2% to 7% by weight, is added to 30%. For all operable sugarsexcept lactose, the desired 3,269,798 Patented August 30, 1966 maximumis about 2%. The phosphoric acid containing the sugar is then heated toabout 350 F. at atmospheric pressure for a sufiicient length of time toincrease the P 0 content to more than The concentration of the acid,containing the stabilizing agent, can be increased to as high as beforethe acid will crystallize out. Then the concentrated acid is admixedwith potassium hydroxide solution to produce a solution or suspension ofsalt in the resulting alkaline liquid. This reaction is exothermic andshould be carried out in a jacketed vessel so that heat can be conductedaway from the reaction mass to prevent the temperature from exceeding F.This temperature is critical since I have found that if it is exceededthe sugar stabilizer loses its ability to function as a stabilizingagent for the composition. The sugar will dehydrate to carbon inalkaline solution.

The sugar stabilizers of the invention have also been found to beparticularly suitable for use with green acid fertilizers. Greenphosphoric acid, sometimes called wet process phosphoric acid, isobtained by treating phosphate rock with sulfuric acid and separatingthe insoluble calcium sulfate formed. This acid is less expensive but ishighly impure and contains many salts, metals and suspended organicmatter. When green acid is combined with potash, ammonia, urea or othernitrogen-bearing material to produce a fertilizer composition, theimpurities form a gelatinous precipitate. Consequently, fertilizers madewith green acid are especially troublesome from the standpoint ofsettling out. The precipitation also changes the concentration of thefertilizer composition (as in the high analysis fertilizer) and presentsproblems in storage or in application of the fertilizer.

The addition of a sugar in accordance with the invention markedlydecreases the tendencies of these impurities to settle out, therebygreatly improving the handling qualities of the fertilizer.

It will be appreciated that the improvement of the invention is achievedat relatively low cost. It is not necessary to use pure sugar, but beetsteep liquor, a byproduct of sugar refining which contains sugars, isentirely suitable. Any unrefined liquors or residues containing theaforementioned operable additives are also applicable for use in thisinvention.

The following specific examples will illustrate the process which isutilized to prepare fertilizers in accordance with the invention, andwill also illustrate some modifications in compositions of theinvention. Except for those steps which are indicated to be critical,these examples are not intended to limit this invention but are setforth merely for purposes of illustration.

Example I Phosphoric acid having concentration of 54% P 0 was treated byadding 2% sucrose in a minimum amount of water. The mixture had aspecific gravity of 1.3. The solution was then heated to 350 F. toincrease the concentration to 76% P 0 This highly concentratedphosphoric acid with the sugar added may be used as a master batch ofsuperacid in preparing specific fertilizer compositions.

To make a fertilizer corresponding to an analysis of 0-35-35 (percent byweight of N, P 0 K 0), 921 grams of the concentrated superacid wereadmixed with 845 grams of potassium hydroxide in 234 grams of water toform 2,000 grams of the liquid composition. These proportions Were usedin mixing laboratory batches but if the amounts are taken in poundsrather than grams, the composition will total one ton of fertilizer. Themixing of the acid and the alkali is carried out in a jacketed vesselthrough which cooling water is passed to maintain the temperature below180 F. This fertilizer, although highly concentrated, is remarkablystable and does not salt out until a temperature of less than 20 F. hasbeen reached. Consequently, it may be sprayed during the normalfertilizing season in any climate without troublesome salting out.

Preparations using maltose or lactose in place of su crose in thisexample have shown identical properties as to salting out temperatures.

Example II The superacid prepared in accordance with Example I andcontaining 2% sucrose was admixed with ammonium hydroxide (29.4% NH inthe proportions of 632 grams of acid to 664 grams NH OH. 704 grams ofwater were added to bring the total to 2,000 grams. The resultant liquidfertilizer had an analysis of 8-24-0, and was found to remain in theliquid phase at temperatures as low as 7 F.

Example III A liquid fertilizer having an analysis of 5-20-20 can beproduced by admixing ammonia and potassium hydroxide with thesuperphosphoric acid prepared in accordance with Example I. Theseingredients are added in the following proportions:

Grams NH 121.2 KOH 500 H PO (80%) 500 880 2 The resultant liquidfertilizer was stable at temperatures down to -20 F.

Nitric acid containing 20% nitrogen may be substituted for the ammoniaas a source of nitrogen without raising the salting out temperature.Urea may also be substituted for the ammonia but will raise the saltingout temperature somewhat.

It will be appreciated that it is impossible to approach the formulationset forth in the examples using normal 54% phosphoric acid.

Example IV Green phosphoric acid (75% P containing 2% glucose wasadmixed with ammonium hydroxide in the correct proportions to produce aliquid fertilizer having an analysis of -30-0. To 1200 grams of thiscomposition were added 200 grams of KCl and 600 grams of water. 6186.Such compositions without the added glucose contain a gelatinousprecipitate. The resulting fertilizer had a salting out temperatureconsiderably lower than 6-18-6 fertilizer produced by conventionalmethods.

Acids containing from 30 to 54% P 0 are also useful in formulating highanalysis fertilizer. From 0.5 to 2% by weight of glucose may be added tosuch phosphoric acids and concentrated by heating to increase the P 0content to 75-80%. To this concentrated acid is added KOH or NH OH withcooling and agitation to produce the desired formulae.

The resulting composition had an analysis of 4 Example V Greenphosphoric acid having a P 0 content of 54.5% was concentrated to P 0 byheating, after 2% by weight of glucose was added. 881 grams of thisconcentrated acid was added to 664 grams of NH OH (29.4% NH to produce astable liq-uid fertilizer having an 8-24-0 formulation.

Example VI Green phosphoric acid (30% P 0 was concentrated to 77% P 0 byheating after 2% by weight of maltose was added. 211 grams of thisconcentrated acid was added to 664 grams of NH OH (29.4% NH to producean 8-240 formulation characterized by exceptional stability with respectto saltin-g out.

I claim:

1. As a composition of matter, a concentrated phosphoric acid solutionof minimally 76% P 0 in admixture with, as a low temperature stabilizingagent, 0.05% to 7% by weight of said acid of a sugar selected from thegroup consisting of sucrose, lactose, maltose and glucose.

2. As a composition of matter, a concentrated phosphoric acid solutionof minimally 76% P 0 in admixture with, as a low temperature stabilizingagent, a sugar selected from the group consisting of sucrose, lactose,maltose and glucose.

3. As a composition of matter, a concentrated phosphoric acid solutionin admixture with, as a low temperature stabilizing agent, 0.05% to 7%by weight of said acid of a sugar selected from the group consisting ofsucrose, lactose, maltose and glucose.

4. As a composition of matter, a concentrated phosphoric acid solutionof minimally 76% P 0 having admixed therewith as a low temperaturestabilizing agent a beet steep liquor.

5. Composition of claim 1 wherein said phosphoric acid is wet processphosphoric acid.

6. Composition of claim 2 wherein said phosphoric acid is wet processphosphoric acid.

7. Composition of claim 3 wherein said phosphoric acid is wet processphosphoric acid.

References Cited by the Examiner UNITED STATES PATENTS 1,768,007 6/1930Sigmund.

1,950,068 3/1934 Spangenberg 71-11 XR 1,950,701 3/1934 Spangenberg 711lXR 2,770,540 11/1956 Vierling 711 XR 2,869,998 1/1959 Vierling 71-1 XR2,929,700 3/1960 Bennett 7125 XR 3,015,552 1/1962 Striplin et al. 711XR3,074,927 1/1963 Soltman et a1 711 XR OTHER REFERENCES Mehltrelter etal. Sequestration by Sugar Acids, Ind. & Eng. Chem., vol. 45, No. 12,Dec. 1953, pp. 2782-84.

OSCAR R. VERTIZ, Primary Examiner.

MAURICE A. BRINDISI, Examiner.

O. F. CRUTCHFIELD, Assistant Examiner.

1. AS A COMPOSITION OF MATTER, A CONCENTRATED PHOSPHORIC ACID SOLUTIONOF MINIMALLY 76% P2O5 IN ADMIXTURE WITH, AS A LOW TEMPERATURESTABILIZING AGENT, 0.05% TO 7% BY WEIGHT OF SAID ACID OF A SUGARSELECTED FROM THE GROUP CONSISTING OF SUCROSE, LACTOSE, MALTOSE ANDGLUCOSE.